.arrow {
  animation-name: beat;
  /*动画名称*/
  animation-duration: 0.8s;
  /*设置秒数*/
  animation-timing-function: ease;
  /* animation-timing-function: linear; */
  /*速度曲线*/
  animation-iteration-count: infinite;
  /*播放次数*/
  animation-direction: alternate;
  /*逆向播放*/
  animation-play-state: running;
  /*正在运行*/
}
.arrow1 {
  animation-delay: 0ms;
}
.arrow2 {
  animation-delay: 250ms;
}
.arrow3 {
  animation-delay: 500ms;
}

@keyframes beat {
  0% {
    transform: translateY(8px);
  }
  90% {
    transform: translateY(-8px);
  }
  100% {
    transform: translateY(-8px);
  }
}